Deep Depolymerization of Lignin via Reductive Acidolysis Yielding Copious Aromatics Thoroughly Revealed by NMR Chromatography

Depolymerization is the cornerstone of lignin valorization. Although this field of research has advanced significantly in the past decade, there are still obstacles preventing large-scale application. The high cost of precious metal catalysts and the use of pressurized hydrogen gas account for some of the limitations. In this work, it is designed to synergize the reductive acidolytic power of hydrogen iodide and the advantageous physicochemical properties of ionic liquids (ILs) as green solvents for the deep depolymerization of real lignin. The results showed that nearly 100% of model compounds were converted in the reaction medium comprising 1-butyl-3 methylimidazolium iodide ([Bmim]I) plus organic acids and a yield up to 81 wt% of depolymerized products of low molecular weights was achieved for real lignins. In addition, a detailed structural assignment of the products was made straightforward by nuclear magnetic resonance chromatography. The advantages of the [Bmim]I/organic acids demonstrated in this study are featured by mild reaction conditions, easy scalability, and cost-effectiveness, paving the way toward the democratization of lignin-derived products.